I have a function that takes a config
object as an argument. Within the function, I also have default
object. Each of those objects contains properties that essentially work as settings for the rest of the code within the function. In order to prevent having to specify all of the settings within the config
object, I use jQuery's extend
method to fill in a new object, settings
with any default values from the default
object if they weren't specified in the config
object:
var config = {key1: value1}; var default = {key1: default1, key2: default2, key 3: default 3}; var settings = $.extend(default, config); //resulting properties of settings: settings = {key1: value1, key2: default2, key 3: default 3};
This works great, but I'd like to reproduce this functionality without the need for jQuery. Is there an equally elegant (or close to) means to do this with plain ol' javascript?
This question is not a duplicate of the "How can I merge properties of two JavaScript objects dynamically?" question. Whereas that question simply wants to create an object that contains all of the keys and values from two separate objects - I specifically want to address how to do this in the event that both objects share some but not all keys and which object will get precedence (the default) for the resulting object in the event that there are duplicate keys. And even more specifically, I wanted to address the use of jQuery's method to achieve this and find an alternative way to do so without jQuery. While many of the answers to both questions overlap, that does not mean that the questions themselves are the same.
The extends keyword is used to create a child class of another class (parent). The child class inherits all the methods from another class. Inheritance is useful for code reusability: reuse properties and methods of an existing class when you create a new class.
The extends keyword can be used to extend the objects as well as classes in JavaScript. It is usually used to create a class which is child of another class. Syntax: class childclass extends parentclass {...}
jQuery | extend() method This extend() Method in jQuery is used to merge the contents of two or more objects together into the first object. Syntax: jQuery.extend( [deep ], target, object1 [, objectN ] )
The _. extend() function is used to create a copy of all of the properties of the source objects over the destination object and return the destination object. The nested arrays or objects will be copied by using reference, not duplicated.
To get the result in your code, you would do:
function extend(a, b){ for(var key in b) if(b.hasOwnProperty(key)) a[key] = b[key]; return a; }
Keep in mind that the way you used extend there will modify the default object. If you don't want that, use
$.extend({}, default, config)
A more robust solution that mimics jQuery's functionality would be as follows:
function extend(){ for(var i=1; i<arguments.length; i++) for(var key in arguments[i]) if(arguments[i].hasOwnProperty(key)) arguments[0][key] = arguments[i][key]; return arguments[0]; }
You can use the ECMA 2018 spread operator in object literals...
var config = {key1: value1}; var default = {key1: default1, key2: default2, key 3: default 3}; var settings = {...default, ...config} //resulting properties of settings: settings = {key1: value1, key2: default2, key 3: default 3};
BabelJS support for older browsers
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